1. Field of the Invention
The present invention relates to a valve operating system in an internal combustion engine, in which an associative operation switchover means capable of switching over the associative operation of a pair of rocker arms disposed adjacent each other and the releasing of the associative operation is provided between a plurality of rocker arms including the rocker arms disposed adjacent each other.
2. Description of the Related Art
Such valve operating systems are conventionally known from Japanese Patent Application Laid-open Nos. 11-13440 and 2-102304 and the like, for example.
In the valve operating system disclosed in the above Japanese Patent Application Laid-open No. 11-13440, a bottomed hole, in which one end of a roller shaft is fitted and fixed, is provided in one of a pair of support walls included in one of a plurality of the rocker arms, which one rocker arm is disposed at one end in the direction of arrangement of the rocker arms, and a through-bore, in which the other end of the roller shaft is fitted and fixed, is provided in the other support wall, with a return spring accommodated in the roller shaft being received at a closed end of the bottomed hole. However, in providing the bottomed hole in the one support wall by drilling, the closed end of the bottomed hole must be subjected to a relieving treatment and hence, the drilling is complicated. Moreover, the size of the rocker arm must be increased by an amount corresponding to the relieving treatment, and the weight of the rocker arm is increased by an amount corresponding to an end wall of the bottomed hole remaining there.
In the valve operating system disclosed in the above Japanese Patent Application Laid-open No. 2-102304, a bottomed hole, in which a limiting member is slidably fitted, is provided in one of a plurality of rocker arms, which is disposed at one end in the direction of arrangement of the rocker arms, and a return spring is mounted between a closed end of the bottomed hole and the limiting member. However, in providing the bottomed hole in the rocker arm by drilling, the closed end of the bottomed hole must be subjected to a relieving treatment and hence, the drilling is complicated. Moreover, the size of the rocker arm must be increased by an amount corresponding to the relieving treatment, and the weight of the rocker arm is increased by an amount corresponding to an end wall of the bottomed hole remaining there.
Accordingly, it is an object of the present invention to provide a valve operating system in an internal combustion engine, wherein in accommodating the return spring of the associative-operation switchover means, the processing or treatment therefore is facilitated, and reductions in size and weight of the rocker arm are provided.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a valve operating system in an internal combustion engine, comprising a first rocker arm having a pair of support walls which support a cylindrical roller shaft at opposite ends thereof, the roller shaft rotatably carrying a roller mounted in rolling contact with a cam provided on a camshaft, the support walls being disposed on opposite sides of the roller, a second rocker arm disposed adjacent the first rocker arm, and an associative-operation switchover means including a switchover pin which is movable between an associatively operating position where the first and second rocker arms are operated in association with each other and an associative-operation releasing position where the switchover pin is separated from the first rocker arm to release the associative operation, the switchover pin being capable of transmitting a hydraulic pressure force acting toward the associatively operating position, a limiting member which is slidably received in the roller shaft in the first rocker arm to abut against the switchover pin, and a coiled return spring accommodated in the roller shaft to exhibit a spring force for biasing the switchover pin toward the associative-operation releasing position, the associative-operation switchover means being provided between a plurality of rocker arms including the first and second rocker arms, wherein the support walls have through-bores coaxially provided therein, in which opposite ends of the roller shaft are fitted and fixed, and a spring-receiving member is mounted to the roller shaft for receiving the return spring which is interposed between the spring-receiving member and the limiting member.
With such arrangement of the first feature, the through-bores are provided in the pair of support walls. Therefore, as compared with the prior art system in which the bottomed hole must be provided by drilling, a relieving treatment is not required, whereby the drilling of the support walls can be facilitated, while enabling a reduction in size of the rocker arms and moreover, the weight of the rocker arms can be reduced by an amount corresponding to the unnecessary end wall.
According to a second aspect and feature of the present invention, in addition to the first feature, a snap ring is detachably mounted to an inner surface of the roller shaft, and the spring-receiving member is ring-shaped, thinner than the snap ring and engaged with the snap ring from an axial inside of the roller shaft. With such arrangement of the second feature, it is easy to mount the spring-receiving member to the roller shaft and further, the spring-receiving member can be formed thinner than the snap ring, whereby the weight of the spring-receiving member can be reduced to contribute to a reduction in weight of the entire rocker arm. Moreover, it can be ascertained from the outside through the ring-shaped spring-receiving member whether the return spring has been accommodated correctly in the roller shaft.
According to a third aspect and feature of the present invention, in addition to the first feature, a driving rocker arm included in the plurality of rocker arms and operatively connected to an engine valve has a roller-accommodating bore provided therein to open vertically, the roller-accommodating bore having a pair of surfaces opposed to an outer peripheral surface of the roller mounted in rolling contact with the cam, the roller being accommodated in the roller-accommodating bore, the roller-accommodating bore being formed to have an area of an opening at a lower end thereof smaller than that at an upper end thereof, with each of the opposed surfaces being comprised of a curved surface portion which is formed to extend between an upper surface of the driving rocker arm and a preset point spaced upwards from a lower surface of the driving rocker arm, the curved surface portion being curved into a circular shape concentric with the roller, an extended surface portion connected at one end thereof to a lower end of the curved surface portion and extending toward the outer peripheral surface of the roller, and a lower surface portion which interconnects the other end of the extended surface portion and the lower surface of the rocker arm and is opposed to a lower portion of the outer peripheral surface of the roller.
With such arrangement of the third feature, by provision of the extended surface portion and the lower surface portion, the thickness of the driving rocker arm at the lower portion of the roller-accommodating bore can be ensured at such a level that a reduction in rigidity can be prevented. Moreover, by forming the extended surface portion to extend from the lower end of the curved surface portion toward the outer peripheral surface of the roller, the lower portion of the surface opposed to the outer peripheral surface of the roller can be disposed at a location closer to the roller to reduce the area of the opening of the lower end of the roller-accommodating bore, thereby enhancing the ability to retain the oil between the opposed surfaces of the roller-accommodating bore and the roller, as compared with a case where the surface opposed to the outer peripheral surface of the roller is formed at a uniform radius of curvature between the upper and lower surfaces of the driving rocker arm.
According to a fourth aspect and feature of the present invention, in addition to the first feature, a driving rocker arm included in the plurality of rocker arms and operatively connected to an engine valve has a roller-accommodating bore provided therein to open vertically, the roller-accommodating bore having a pair of surfaces opposed to an outer peripheral surface of the roller mounted in rolling contact with the cam, the roller being accommodated in the roller-accommodating bore, an opening edge at the lower end of the roller-accommodating bore being comprised of a pair of parallel portions parallel to each other and corresponding to the opposite side surfaces of the roller, and a pair of curved portions which are opposed to the outer peripheral surface of the lower portion of the roller and interconnect the parallel portions, the curved portions being bulged on a side opposite from the outer peripheral surface of the lower portion of the roller, opposite ends of the curved portions being smoothly connected to the parallel portions.
With such arrangement of the fourth feature, a stress concentration can be prevented from being produced in a connection between the parallel portion which is a portion opposed to the side surface of the roller and the curved portion which is a portion opposed to the outer peripheral surface of the roller in the opening edge at the lower end of the roller-accommodating bore, thereby contributing to an enhancement in durability of the driving rocker arm.
According to a fifth aspect and feature of the present invention, there is provided a valve operating system in an internal combustion engine, comprising an associative-operation switchover means including a switchover pin which is movable between an associatively operating position where the switchover pin is located astride first and second rocker arms disposed adjacent each other to permit the first and second rocker arms to be operated in association with each other and an associative-operation releasing position where the switchover pin is separated from the first rocker arm to release the associative operation, the switchover pin being capable of transmitting a hydraulic pressure force acting toward the associatively operating position, a limiting member which is slidably received in the first rocker arm to abut against the switchover pin, and a coiled return spring accommodated in the first rocker arm to exhibit a spring force for biasing the switchover pin toward the associative-operation releasing position, the associative-operation switchover means being provided between a plurality of rocker arms including the first and second rocker arms, wherein the first rocker arm is provided with a through-bore in which the limiting member is slidably fitted; a snap ring is detachably mounted to an inner surface of an outer end of the through-bore; and a ring-shaped spring-receiving member thinner than the snap ring is engaged with the snap ring from an axial inside of the through-bore, the return spring being mounted between the limiting member and the spring-receiving member.
With such arrangement of the fifth feature, the snap ring engaged with the outer surface of the ring-shaped spring-receiving member inserted in the through-bore is detachably mounted to the inner surface of the outer end of the through-bore. Therefore, as compared with the prior art system in which the bottomed hole must be provided by drilling, a relieving treatment is not required, whereby the drilling of the rocker arm can be facilitated, while enabling a reduction in size of the rocker arm and moreover, the weight of the rocker arm can be reduced by an amount corresponding to the unnecessity of an end wall. In addition, it is easy to mount the spring-receiving member in the through-bore and further, the spring-receiving member can be formed thinner than the snap ring, whereby the weight of the spring-receiving member can be reduced to contribute to a reduction in weight of the entire rocker arm. Moreover, it can be ascertained from the outside through the ring-shaped spring-receiving member whether the return spring has been accommodated correctly in the roller shaft.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.